1. Field of the Invention
The present invention relates to a radar system for detecting a target such as a vehicle traveling in front of or behind another vehicle.
2. Description of the Related Art
A vehicle including a following-distance alarm system that issues an alarm when the distance between the vehicle and another vehicle traveling in front of the vehicle is decreased, and that performs braking control as required is disclosed in Japanese Unexamined Patent Application Publication No. 11-339198.
In the following-distance alarm system, the operation of a radar system is stopped when the speed of the vehicle is decreased, in order to extend the life of a laser diode used for a scan-laser radar system. The radar is activated when the movement of the vehicle traveling in front is detected by using a sub-sensor, such as a CCD camera or an ultrasonic sensor.
In the following-distance alarm system, however, the operation of the radar is stopped when the speed of the vehicle is less than a predetermined speed. Therefore, another sub-sensor designed specifically for detecting a start of the vehicle traveling in front is needed. Accordingly, the configuration of the alarm system becomes complicated, and the cost is increased. Further, a target is detected over a predetermined range by scanning the direction of a beam of a detection signal. Sometimes, such scanning becomes unnecessary according to the vehicle speed.
In order to overcome the problems described above, preferred embodiments of the present invention provide a radar system which eliminates the above-described sub-sensor and which uses beam scanning very effectively.
According to a preferred embodiment of the present invention, a radar system includes a detection-control circuit for transmitting and receiving a detection signal and for detecting a relative position or a relative speed to a target, a scanning unit for scanning the direction of a beam of a detection signal over a predetermined range, and a beam-scanning control unit. The beam-scanning control unit switches the state of the scanning unit between a resting state wherein the direction of the beam is fixed to a predetermined position, for example, the center position in the predetermined range, while the detection-control circuit continues detection controlling, and a scanning state wherein the direction of the beam is scanned over the predetermined range. Accordingly, detection controlling can be performed when beam scanning is stopped, whereby a sensor designed specifically for detecting the start of a vehicle traveling in front becomes unnecessary, for example.
Preferably, in the radar system, the beam-scanning control unit switches the scanning unit into the scanning state when the moving speed of a vehicle in which the radar system is mounted is equal to or greater to a predetermined speed. Further, the beam-scanning control unit switches the scanning unit into the resting state when the moving speed is less than the predetermined speed. Accordingly, beam scanning is performed only when the vehicle is traveling at a high speed, and is stopped when the vehicle is traveling at a low speed in order to prolong the life of the scanning unit. As a result, the life of the radar system is prolonged, and the reliability thereof is easily increased.
Preferably, in the radar system, the beam-scanning control unit switches the scanning unit into the scanning state when the vehicle having the radar system is traveling on a highway, and switches the scanning unit into the resting state when the vehicle is not traveling on a highway. Accordingly, beam scanning is performed only in case of necessity and is stopped at other times, so that the life of the scanning unit is prolonged.
Preferably, the beam-scanning control unit switches the scanning unit into the scanning state when the detection-control circuit detects a new target or the relative movement of the target during the resting state of the scanning unit. Accordingly, beam scanning can be automatically started and can be stopped until a need arises. Thus, the life of the scanning unit is prolonged.
Preferably, in the radar system, the direction of the beam scanned by the scanning unit is in a horizontal plane, or in a plane at a predetermined tilt angle. Accordingly, the moving target can be captured over the scanning range, and can be captured for a relatively long time.
Preferably, in the radar system, the direction of the beam scanned by the scanning unit is in a substantially vertical plane. Accordingly, the existence range of the target in the scanning range, that is, the height of the target can be detected. Further, the type of the target can also be identified.
Other features, elements, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments thereof with reference to the attached drawings.